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MathNet 2025-part-01 — 187 problems (EN–VI) Question 128

Math Olympiad Vault · MathNet 2025-part-01 — 187 problems (EN–VI)

Question 128

Let triangle $ABC$ be inscribed in a circle $\omega$, and let $M$ be the midpoint of arc $AB$ that does not contain point $C$. Let the tangent to $\omega$ at point $B$ intersect line $AC$ at point $P$. Let line $PM$ intersect $\omega$ again at point $G$. The tangent to $\omega$ at point $G$ intersects line $BC$ at point $Q$. Let lines $AB$ and $CG$ intersect at point $K$. If points $P, Q, K$, and $C$ lie on a common circle, prove that lines $KQ$ and $GB$ are parallel.

(Khulan Tumenbayar)